I’m often asked the same questions by different people so I thought it useful to publish some of the emails I get and the answers for everyone.
Stopping Caterpillars Eating the Brassicas
“I am an avid reader of your website, its great! [NB – Flattery gets you everywhere]
I wondered if you can help me, this year and last year my cabbages , etc were ruined by the white butterfly laying eggs etc etc. ending up in the plants getting ruined again for a second year and this was with protecting the plants with netting.
I wondered if there was anything I can spray on the vegetables next year ?
I don’t think I can go through a 3rd year of ruined vegetables.
Thank you in advance.”
Netting is usually effective but it only takes a little gap for one butterfly to get through and one butterfly can lay an awful lot of eggs. Vigilance is the best defence, check the netting has no gaps and is secure at all times. Check the underside of the leaves for the eggs and rub them off if found.
I know that’s a counsel of perfection and often the first you realise is that leaves have been eaten and there’s a Mongol hoard of caterpillars munching your crop. You can pick them off by hand (we call these a treat for the chickens) but it’s time consuming and you always seem to miss a few.
I used to recommend Derris which was made from natural products, considered very safe and was effective but then some American found some potential risk from a similar product and it came off the list. So that’s out.
The best bet is to go to a decent garden centre and look at what is available now, checking that it is approved for food crops. Always read the label very carefully and note period between spraying and eating allowed and how many times you can use the product. Some just once, some three times or more.
I don’t like sprays, but sometimes it’s the lesser of two evils: spray or no crop.
Seed Saving and Propagating Leeks & Onions
“One quick ask…..I can see how to save my shallots until next spring to split up and set again to get an increasingly better strain to suit my plot in Derbyshire…..(I would think garlic would be the same)….. but how do I do that with onions and leeks as you mentioned in your newsletter? Do I let a few go to seed and then save the seed? It’s not as though onions & leeks can be split up like shallots & garlic can. I’d be really interested to know”
A quick ask but a longer answer, I’m afraid. With leeks, the usual way is to grow from bought in seed and then vegetative propagation of the best specimens. There’s an article explaining this process on the site here: Vegetative Propagation of Blanch Leeks
I can’t really cover propagating onions in a quick email so watch out for
an article on the site soon. We’ve an article now – How to Propagate Onions (Seed Saving)
I once saw an allotment program from Wales that recommended using rhubarb leaves soaked in a container and after a couple of weeks spraying or use a watering can to apply to your cabbages, it appeared to work as when the cabbage white butterflies approached they did not land on the cabbages and left the cabbages alone
@dwtomo: Some of these old methods work well but some are just a myth – like burying a piece of rhubarb to ward off clubroot. There’s an article on home remedies that you might find helpful here: Home Made Pesticides
If you’ve got a prize onion and more time than sense, googling scale propagation will provide you with a few hours of entertainment!
I’ve had great success with Bacillus thuringiensis. This was the bacterium which was killing off the French silk industry until Louis Pasteur demonstrated the culprit and got the silk farmers to practise better hygiene. My stuff , BioBT, is very old, so may not be available. The powder contains bacterial spores and a wetting agent; sprayed on the caterpillars eat contaminated leaves and then die within days and won’t kill anything but caterpillars. I have a pigeon problem so use 1cm netting all season. Even that keeps most of the adults away .